3.4 Monohybrid and Test Cross Notes

Document technical information

Format ppt
Size 4.2 MB
First found May 22, 2018

Document content analysis

Category Also themed
Language
Type
not defined
Concepts
no text concepts found

Persons

Organizations

Places

Transcript

Monohybrid Cross
IB ASSESSMENT STATEMENT
• Define genotype, phenotype, dominant allele, recessive
allele, codominant alleles, locus, homozygous,
heterozygous, carrier and test cross.
Phenotype & Genotype
• Phenotype – the physical characteristics
of an organism (example: blue eye color)
Phenotype & Genotype
• Genotype – the alleles possessed by an
organism (example: inheriting two blues
alleles on from each parent)
Dominant & Recessive Allele
Dominant Allele – An allele that dominants
over a recessive allele. Represented in
genetics with a capital letter (example the
capital letter B could represent the
dominant allele for brown eyes).
Dominant & Recessive Allele
Recessive Allele - An allele that does NOT
dominate over other traits. Represented in
genetic by a lower case letter (example
the lower case letter b could represent the
allele for blue eyes)
Types of Genotypes
• Homozygous Dominant: An organism
having two identical dominant alleles.
Represented in genetic by having two upper
case letters. (example: BB represents a
person that has two alleles for brown eyes)
Types of Genotypes
• Homozygous Recessive: An organism
having two identical recessive alleles.
Represented in genetic by having two lower
case letters. (example: bb represents a
person that has two alleles for blue eyes)
Types of Genotypes
Heterozygous: An organism having two
different alleles for a trait, one recessive and
one dominant. Represented in genetic by
having one upper case and one lower case
letters. (example: Bb represents a person
that has a dominant alleles for brown eyes
and a recessive allele for blue eyes).
IB Assessment Statement
• Determine the genotypes and phenotypes of the
offspring of a monohybrid cross using a Punnett grid.
The grid should be labelled to include parental
genotypes, gametes, and both offspring genotype and
phenotype.
Punnet Square/ Grid
Punnet Square / Grid is a grid or table that
shows all the possible outcomes between
a cross between a male in female
organisms
Example
• F0: Cross a heterozygote pea plant with smooth seeds with a plant
with wrinkled seeds.
–
–
–
–
Select Symbols the alleles:
Write the cross:
Gametes each parent can produce:
Make a punnet square.
F1:
–
–
–
What percent are heterozygous?
What percent are smooth?
What percent are wrinkled?
P-square Practice Question #1
Let's say that in seals, the gene for the length of the whiskers has two
alleles. The dominant allele (W) codes long whiskers & the recessive allele
(w) codes for short whiskers. Cross two long-whiskered seals, one that is
homozygous dominant and one that is heterozygous?
– The Symbols (letters you will use) ______________________
– The Cross (the parent’s genotypes)_________________________
– The Punnett square:
P-square Practice Question #2
In purple people eaters, one-horn is dominant and no horns is recessive. Draw
a Punnet Square showing the cross of a purple people eater that is
heterozygous for horns with a purple people eater that does not have
horns.
–
–
–
The Symbols (letters you will use) ______________________
The Cross (the parent’s genotypes)_________________________
The Punnett square:
Test Crosses
Problem:
• When an organism has a shows a
dominant phenotype (example: Brown
Eyes) it is not always possible to know if
this organism is has a heterozygote
genotype (Bb) or Homozygote dominant
genotype (BB) because the phenotype
(physical appearance) it the same for both
genotypes.
Test Cross
Solution:
• To determine the genotype of an
organism showing a dominant phenotype
a test cross is used.
What is a test cross?:
In a test cross an individual that might be
heterozygous or homozygous dominant is
crossed with an individual that is
homozygous recessive.
How it works?
If you cross a homozygous recessive
organism with a homozygous dominant
organism all the offspring will have the
dominant phenotype.
Example: Black fur color is dominant to white fur color in sheep. A
homozygous dominant black sheep is cross with a homozygous
recessive white sheep.
• The Symbols (letters you will use) ______________________
• The Cross (the parent’s genotypes)_________________________
• The Punnett square:
If you cross a homozygous recessive
organism with a heterozygote 50% of the
offspring will have the dominant
phenotype and 50% will have the
recessive phenotype.
Example: Black fur color is dominant to white fur color in sheep. A
heterozygous black sheep is cross with a homozygous recessive
white sheep.
•
The Symbols (letters you will use) ______________________
•
The Cross (the parent’s
genotypes)_________________________
•
The Punnett square:

Similar documents

×

Report this document